PHASE-BEHAVIOR AND LIGHT-SCATTERING OF THE SYSTEM DODECYLDIMETHYLAMINOXIDE, NORMAL-HEXANOL AND WATER IN THE VERY DILUTE REGION

Solutions of Dodecyldimethylaminoxide (DDMAO), n-hexanol and water show a phase behavior which is found to be typical for many surfactant-alcohol-water systems with lamellar phases. Three types of lamellar phases and three types of isotropic low viscous clear phases which exhibit extreme flow birefringence (L3-phases) are found at room temperature. Both a hexanol-rich (L(alpha-h)) and a hexanol-poor lamellar phase (L(alpha-l)) can be diluted to iridescent solutions with bright colors. The iridescent L(alpha-h) phase is of low viscosity and forms quickly, the higher viscous L(alpha-l) phase needs 600 hours until the iridescence can be observed. - UV-Vis and classical light scattering measurements show that the interlamellar structures or spacings of the L(alpha-l) phase are strongly and those of the L.h phase are weakly fluctuating. The L(alpha-h) phase is much more sensitive to added electrolyte than the L(alpha-l) phase. The L(alpha-l) phase seems to be the type of iridescent phases which can be found with some ionic surfactant-water systems. - An intermediate lamellar phase exists between the L(alpha-h) and the L(alpha-l) phase with a second order or kinetically controlled phase transition. At the lower concentration limit (DDMAO concentration around 50 mmol/l) this intermediate phase needs several months for the formation. - The L(alpha-h) phase is accompanied at some higher hexanol concentration by a L3 phase. This phase transforms quickly to an iridescent phase immediately after shear stress. Depending on concentration and temperature this iridescent phase remains stable for a few minutes to several hours. The second isotropic phase with extreme flow birefringence exists below the L(alpha-l) phase. Dilution of the intermediate lamellar phase leads to an intermediate phase of type L3 which is not in a thermodynamic equilibrium state. - The L(alpha-l) phase and the intermediate lamellar phase give slow torsion waves whose propagation can be observed between crossed polarizers. The rheologic behavior which leads to these shear waves is discussed.